Defence Minister John Faulkner has ordered the Defence Department to remove references to biblical passages marked on gunsights being used by Australian troops in Afghanistan.

References to New Testament verses were etched onto the gunsights by the American manufacturer, Trijicon, and the department says it was unaware of their meaning at the time of purchase.

The firm says it has been inscribing references to Bible verses as part of the serial numbers on its products for more than 20 years, during which time they have been used by Australian troops as well as the US and British militaries.

The Australian Defence Force has just over 1,000 of the sights and Senator Faulkner says he was shown some of them during a visit to Victoria Barracks yesterday.

"I understand the concerns about the issue," he said. "I have asked Defence to examine the options available to deal with this matter without compromising the safety of our troops and critically important capabilities."

Overnight Trijicon said it would supply the US military with 100 kits "to enable the removal of the references that are already on products that are currently deployed" by US forces.

Critics have charged that the company is putting troops in danger in Muslim-majority nations where the Western military presence is already bitterly resented.

An ADF spokeswoman said the Department of Defence was unaware of the significance of the serial numbers when it purchased the sights.

"The sights were procured because they provide mature technology which is highly reliable, in wide use by our allies, and best meets Defence requirements," she told the ABC.

"The Department of Defence is very conscious of the sensitivities associated with this issue and is assessing how to address these as soon as practicable."

Among the coded inscriptions on Trijicon gunsights are JN8:12, an apparent reference to John 8:12: "Then spake Jesus again unto them, saying, I am the light of the world: he that followeth me shall not walk in darkness, but shall have the light of life."

Another made reference to Psalms 27:1: "The Lord is my light and my salvation; whom shall I fear?".

The company currently has a multi-year, $US660 million ($731 million) contract with the US Marines and other contracts with the US Army.

Just under 300,000 of the gun sights are currently fielded by American forces - 220,000 by the Marines and between 70,000 and 75,000 by the army, a Pentagon official said, speaking on condition of anonymity.

Besides providing kits, the company said it would remove the biblical references on all US military products that have not yet been shipped, and stop inscribing them on gun sights in the future.

Trijicon said it had taken the step "in response to concerns raised by the [US] Department of Defence" and to "ensure the war-time production needs of the troops are met as quickly as possible."

It also offered other international military forces using its products - which include the British military and the New Zealand defence forces - the option to remove the references.

The Pentagon said earlier it was "disturbed" after reports emerged this week about the inscriptions. The Marine Corps and the Army have launched a review.

The practice appeared to be a direct violation of a US Central Command general order issued after the 2003 US-led invasion of Iraq that strictly prohibits "proselytising of any religion, faith or practice."

US Army spokesman Gary Tallman earlier said that "we were unaware of these coded biblical references until several days ago," adding that the service branch currently has about 100,000 of the scopes in its inventory.

"It is not the policy of the Department of Defence to put religious references of any kind on its equipment," he added.

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